The present invention relates generally to clutches and, more specifically, to fluid friction clutches.
Fluid friction clutches are generally known in the art and are often employed in conjunction with radiator fans of combustion engines. Such clutches may serve to control the rotational speed of cooler or radiator fans in response to temperature. Suitable temperature sensing devices for use with fluid friction clutches include bi-metal strips.
However, in typical fluid friction clutches of this type the opening from the clutch fluid supply or reservoir to the clutch fluid working space is in a closed position when the combustion engine is operating at low or idling speeds. Thus, very little clutch fluid remains in the working space, and the fan rotational speed is comparatively low during idling. As a result, when a sudden increase in power occurs there is a significant delay in supplying clutch fluid to the working space and increasing fan rotational speed. This permits the combustion engine to undesirably overheat.
Published European Patent Application No. (EP 70 111 A1) shows another fluid friction clutch having a single inlet bore in the intermediate wall between the working space and the fluid supply space to influence the rotationally dependent function of the clutch. Since a constant flow of clutch fluid must remain, this single inlet bore must have a relatively large diameter. However, this arrangement does not permit even wetting of the clutch disk in the temperature dependent controlled friction clutch. Furthermore, the idling speed of the fan cannot be evenly varied or steplessly increased by changing the diameter or size of this single bore because at and above a certain diameter the idling speed increases erratically.
It is therefore an object of the present invention to provide an inexpensive improved fluid friction clutch.
Another object is the provision of a fluid friction clutch having an increased idling speed with a minimum of structural detail.
A further object is to provide a fluid friction clutch for a combustion engine radiator fan having a minimal delay in increasing fan rotational speed in response to increases in combustion engine power.
These and other objects of the present invention are achieved in the provision of a fluid friction clutch having an intermediate wall, disposed in a housing and separating the clutch fluid supply or storage space and the clutch fluid working space, with a plurality of overflow openings therein at circumferentially spaced locations. The clutch fluid primarily enters the working space from the storage space through a controllable supply inlet opening in the intermediate wall. The supply inlet is thermostatically controlled by a bi-metallic element. A rotating clutch disk is provided in the working space, and at least one clutch fluid return bore is provided in the intermediate wall in the region adjacent the outer circumference of the clutch disk. These return bores provide return guidance for clutch fluid into the storage space.
It has been found to be particularly advantageous to dispose the overflow openings of the present invention toward the outer circumference of the intermediate wall and equally spaced about that circumference. With this arrangement, the clutch fluid within the storage space is formed into a rotating water ring within the housing based upon the rotation of the clutch housing and enters the working space through the overflow openings. It has been determined that by such measures, the idling speed may be increased about 200 to 600 RPM without extensive and expensive structural changes in the clutch.
The even distribution of the overflow openings about the circumference of the adjacent clutch disk results in an even wetting of the clutch disk. Thereby, oil circulation is largely independent from the air temperature. In preferred embodiments of the present invention, three to ten overflow openings are provided and arranged in the central or intermediate disk of the intermediate wall. The controllable supply inlet is also provided in that intermediate disk. This disk is inserted or mounted in a central recess of the cover for the clutch housing. This arrangement provides for ease of assembly and disassembly, particularly for applying additional overflow openings or retrofitting the present invention into existing fluid friction clutches.
The precise size of the overflow openings and particular radial arrangement may be readily determined according to the desired fluid supply in the working space of particular embodiments. It has been found to be particularly advantageous in some embodiments to provide overflow openings each of a 3 mm maximum diameter, and preferably of a 1.5 to 2.8 mm diameter, and whereby the cinematical viscosity of the clutch fluid lies in the range of 30,000 to 50,000 cSt (centiStokes).
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.